Multi-Layer Nano-Particle Preparation and Applications

ABSTRACT

A multi-layer nano-particle composition including a polymer core and at least two additional layers is provided. The nano-particles have a mean average diameter less than about 100 nm. The nano-particles can be modified via, for example, hydrogenation or functionalization. The nano-particles can be advantageously incorporated into rubbers, elastomers, and thermoplastics.

This application is a divisional application of U.S. Ser. No. 10/331,841(filed Dec. 30, 2002), which is a continuation-in-part of U.S. Ser. No.10/223,393 filed Aug. 19, 2002, which is a continuation-in-part of U.S.Ser. No. 09/970,830 (filed Oct. 4, 2001), now U.S. Pat. No. 6,437,050and U.S. Ser. No. 10/038,748 (filed Dec. 31, 2001).

BACKGROUND OF THE INVENTION

The present invention relates to polymer nano-particles, methods fortheir preparation, and their use as, for example, additives for rubber,including natural and synthetic elastomers. The invention advantageouslyprovides several mechanisms for surface modification, functionalization,and general characteristic tailoring to improve performance in rubbers,elastomers, and thermoplastics.

Polymer nano-particles have attracted increased attention over the pastseveral years in a variety of- fields including catalysis, combinatorialchemistry, protein supports, magnets, and photonic crystals. Similarly,vinyl aromatic (e.g. polystyrene) microparticles have been prepared foruses as a reference standard in the calibration of various instruments,in medical research and in medical diagnostic tests. Such polystyrenemicroparticles have been prepared by anionic dispersion polymerizationand emulsion polymerization.

One benefit of using nano-particles as an additive in other materials isthat they can be discrete particles uniformly dispersed throughout ahost composition. Nano-particles preferably are monodisperse in size anduniform in shape. However, controlling the size of nano-particles duringpolymerization and/or the surface characteristics of such nano-particlescan be difficult. Accordingly, achieving better control over the surfacecomposition of such polymer nano-particles also is desirable.

Rubbers may be advantageously modified by the addition of variouspolymer compositions. The physical properties of rubber moldability andtenacity are often improved through such modifications. Of course,however, the indiscriminate addition of nano-particles to rubber maycause degradation of the matrix material, i.e., the rubber,characteristics. Moreover, it is expected that primarily through theselection of nano-particles having suitable size, material composition,and surface chemistry, etc., will improve the matrix characteristics.

In this regard, development of nano-particles having a surface layerwhich would be compatible with a wide variety of matrix materials isdesirable because discrete particles could likely disperse more evenlythroughout the host to provide a uniform matrix composition. However,the development of a process capable of reliably producing acceptablenano-particles has been a challenging endeavor. For example, thesolubility of various monomers in traditional alkane solvents has madesolution polymerization a difficult process by which to achievenano-particles having tailored variety of surface layers. Moreover, thedevelopment of a solution polymerization process which produces reliablenano-particles, particularly nano-particles advantageously employed inrubber compositions, has been elusive.

SUMMARY OF THE INVENTION

A multi-layer nano-particle composition including a poly(alkenylbenzene)core and at least two additional layers is provided. The nano-particleshave a mean average diameter less than about 100 nm. As used herein, theuse of the phrase “additional layers” reflects, for example, layersformed of divergent monomers or of the same monomers but havingdiffering characteristics including molecular weight, vinylmodification, functionalization, etc. As one effective usualcharacteristic of the present nano-particles, they can be described asonion-like in view of their multiple layers.

A process for forming a multi-layer nano-particle is also provided. Theprocess includes initiating the block copolymerization of a firstmonomer in a hydrocarbon solvent to form a living polymerizationmixture. At least a second monomer is then added to the polymerizationmixture and polymerized to form a living polymer chain. Analkenylbenzene monomer is also added to the polymerization mixture andallowed to polymerize onto the living polymer chain. The living polymerchains are made to aggregate to form micelles and at least onecrosslinking agent is added to the polymerization mixture to formcrosslinked nano-particles having a poly(alkenylbenzene) core and atleast two additional layers.

A rubber composition including an elastomer, nano-particles, carbonblack, silica and a curing agent having low shrinkage properties is alsoprovided. A process for preparing the rubber compound is similarlyprovided. Such compound shows its relatively high hysterisis, goodtensile strength, good tear strength, strong resistance to creep, hightemperature resistance, and good aging properties. A process of makingthe rubber compound for engine mount applications is similarly provided.

Herein throughout, unless specifically stated otherwise:

“vinyl-substituted aromatic hydrocarbon” and “alkenylbenzene” are usedinterchangeably; and

“rubber” refers to rubber compounds, including natural rubber, andsynthetic elastomers including styrene-butadiene rubber, ethylenepropylene rubber, etc., which are known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depicting the principle of formation ofmulti-layer nano-particles.

FIG. 2 is a transmission electron microscopy (TEM) photograph ofmulti-layer nano-particles produced in accordance with EXAMPLE 1.

FIG. 3 is a TEM photograph of hydrogenated multi-layer nano-particlesproduced in accordance with EXAMPLE 2.

FIG. 4 is a TEM photograph of multi-layer nano-particles produced inaccordance with EXAMPLE 3.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

General Nano-Particle Process of Formation

This application incorporates by reference U.S. Ser. No. 09/970,830(filed Oct. 4, 2001), now U.S. Pat. No. 6,437,050, and U.S. Ser. No.10/038,748 (filed Dec. 31, 2001) and U.S. Ser. No. 10/223,393 (filedAug. 19, 2002).

One exemplary polymer nano-particle of the present invention is formedfrom multiblock polymer chains having at least three blocks selectedprimarily from poly(conjugated diene) block and poly(alkenylbenzene)blocks. Of course, the various monomer constituents may be present to alimited extent in the blocks of another selected monomer. In addition,the present invention anticipates nano-particles wherein one or morelayers are formed of a random copolymer of two or more monomer units.

The poly(alkenylbenzene) blocks may be crosslinked to form the desirednanoparticles. The nano-particles have diameters—expressed as a meanaverage diameter—that are preferably less than about 100 nm, morepreferably less than about 75 nm, and most preferably less than about 50nm. The nano-particles preferably are substantially monodisperse anduniform in shape. The dispersity is represented by the ratio of M_(w) toM_(n), with a ratio of 1 being substantially monodisperse. The polymernano-particles of the present invention preferably have a dispersityless than about 1.3, more preferably less than about 1.2, and mostpreferably less than about 1.1. Moreover, the nano-particles arepreferably spherical, though shape defects are acceptable, provided thenano-particles generally retain their discrete nature with little or nopolymerization between particles.

The nano-particles are preferably formed via dispersion polymerization,although emulsion polymerization is also contemplated. Hydrocarbons arepreferably used as the dispersion solvent. Suitable solvents includealiphatic hydrocarbons, such as pentane, hexane, heptane, octane,nonane, decane, and the like, as well as alicyclic hydrocarbons, such ascyclohexane, methyl cyclopentane, cyclooctane, cyclopentane,cycloheptane, cyclononane, cyclodecane and the like. These hydrocarbonsmay be used individually or in combination. However, as more fullydescribed herein below, selection of a solvent in which one polymerforming the nano-particles is more soluble than another polymer formingthe nano-particles is important in micelle formation.

With respect to the monomers and solvents identified herein,nano-particles are formed by maintaining a temperature that is favorableto polymerization of the selected monomers in the selected solvent(s).Preferred temperatures are in the range of about −40 to 250° C., with atemperature in the range of about 0 to 150° C. being particularlypreferred. As described in more detail below, the interaction of monomerselection, temperature and solvent, facilitates the formation of blockpolymers which form micelles and ultimately the desired nano-particles.

According to one embodiment of the invention, a first multiblock polymeris formed of at least vinyl aromatic hydrocarbon monomers and conjugateddiene monomers in the hydrocarbon solvent. The multiblock polymercontains at least one block that is soluble in the dispersion solvent,preferably a conjugated diene monomer, and at least an end block whichis less soluble in the dispersion solvent, preferably avinyl-substituted aromatic hydrocarbon monomer. Moreover, in oneembodiment, a vinyl-substituted aromatic hydrocarbon monomer is chosenthe polymer of which is generally insoluble in the dispersion solvent.

As is known in the art, such a multiblock copolymer may be formed byliving anionic polymerization, in which each block is formed by adding anew monomer charge to a living polymerization mixture in whichpolymerization is substantially complete.

Additionally, other blocks are incorporated into the block copolymer,including additional poly(conjugated diene) blocks orpoly(alkenylbenzene) blocks, as well as other blocks such aspoly(alkylene) blocks. Other suitable monomer units include ethyleneoxide, methyl methacrylate, nitrites, acrylates, and mixtures thereof.

Another method of forming substantially multiblock polymers is theliving anionic copolymerization of a mixture of monomers, such as aconjugated diene monomer and a vinyl-substituted aromatic hydrocarbonmonomer in a hydrocarbon solvent, particularly, in the absence ofcertain polar additives, such as ethers, tertiary amines, or metalalkoxides which could otherwise effect the polymerization of theseparately constituted polymer blocks. Of course, certain advantages maybe achieved via a random polymerization of at least one block of thepolymer.

However, since more than one additional polymer block is to beincorporated into the nano-particle, it may be preferred to utilize thefirst-described polymerization technique, wherein subsequent monomerunits are added after substantially complete polymerization of eachprevious block.

Such multi-block polymers, are believed to aggregate to formmicelle-like structures, with for example, vinyl-substituted aromaticblocks directed toward the centers of the micelles and all other blocksas tails extending therefrom. It is noted that a further hydrocarbonsolvent charge or a decrease in polymerization mixture temperature mayalso be used, and may in fact be required, to obtain formation of themicelles. Moreover, these steps may be used to take advantage of thegeneral insolubility of the vinyl-aromatic blocks. An exemplarytemperature range for micelle formation is between about 0 and 100° C.,more preferably between about 20 and 80° C.

Although the above describes formation of multi-block polymers prior tomicelle formation, it is noted that after the micelles have formed,additional monomer charge(s), such as conjugated diene monomer and/orvinyl-substituted aromatic hydrocarbon monomer, can be added to thepolymerization mixture as desired. In this manner, multi-block polymersmay again be formed when only diblock polymers form the micelles.Moreover, it is feasible to form the micelles of the block co-polymerswith a further monomer(s) charge thereafter.

After formation of the micelles, a cross-linking agent is added to thepolymerization mixture. Preferably a crosslinking agent is selectedwhich has an affinity to the vinyl-substituted aromatic hydrocarbonmonomer blocks and migrates to the center of the micelles due to itscompatibility with the monomer units and initiator residues present inthe center of the micelle and its relative incompatibility with thedispersion solvent and monomer units present in the outer layer of themicelle. The crosslinking agent crosslinks the center core of themicelle (i.e. alkenylbenzene) to form the desired nano-particle.Consequently, nano-particles are formed from the micelles with a coreincluding, for example, styrene monomer units and a surface layerincluding, for example, butadiene monomer units. Reference to FIG. 1schematically depicts -the above-described process, including a Step A(polymerization); Step B (micelle formation); and Step C (nanoparticleformation).

The conjugated diene monomers contemplated for the block polymer arethose soluble in non-aromatic hydrocarbon solvents. C₄-C₈ conjugateddiene monomers are the most preferred. Exemplary conjugated dienemonomers include 1,3-butadiene, isoprene, and 1,3-pentadiene.

Vinyl-substituted aromatic hydrocarbon monomers include styrene,α-methylstyrene, 1-vinyl naphthalene, 2-vinyl naphthalene, 1-α-methylvinyl naphthalene, 2-α-methyl vinyl naphthalene, vinyl toluene,methoxystyrene, t-butoxystyrene, and the like, as well as alkyl,cycloalkyl, aryl, alkaryl, and aralkyl derivatives thereof, in which thetotal number of carbon atoms in the combined hydrocarbon is generallynot greater than 18, as well as any di- or tri-vinyl substitutedaromatic hydrocarbons, and mixtures thereof.

The multiblock polymer, preferably has M_(w) of about 5,000 to1,000,000, more preferably between about 10,000 and 100,000. A typicalmultiblock polymer will be comprised of 5 to 8% by weight conjugateddiene and 95 to 5% by weight vinyl-substituted aromatic hydrocarbon,more preferably 30 to 70% by weight, and most preferably 40 to 60% byweight of each contributed monomer type, with the weight beingdistributed among multiple blocks if more than one block of eachcontributed monomer type is present.

The micelle formed by the above described polymerization is preferablycrosslinked to enhance the uniformity and permanence of shape and sizeof the resultant nano-particle. Preferred crosslinking agents are di- ortri-vinyl-substituted aromatic hydrocarbons. However, crosslinkingagents which are at least bifunctional, wherein the two functionalgroups are capable of reacting with vinyl-substituted aromatichydrocarbon monomers are acceptable. A preferred crosslinking agent isdivinylbenzene (DVB).

A 1,2-microstructure controlling agent or randomizing modifier isoptionally used to control the 1,2-microstructure in the conjugateddiene contributed monomer units, such as 1,3-butadiene, of thenano-particle. Suitable modifiers include hexamethylphosphoric acidtriamide, N,N,N′,N′-tetramethylethylene diamine, ethylene glycoldimethyl ether, diethylene glycol dimethyl ether, triethylene glycoldimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran,1,4-diazabicyclo [2.2.2] octane, diethyl ether, triethylamine,tri-n-butylamine, tri-n-butylphosphine, p-dioxane, 1,2-dimethoxy ethane,dimethyl ether, methyl ethyl ether, ethyl propyl ether, di-n-propylether, di-n-octyl ether, anisole, diberizyl ether, diphenyl ether,dimethylethylamine, bis-oxalanyl propane, tri-n-propyl amine, trimethylamine, triethyl amine, N,N-dimethyl aniline, N-ethylpiperidine,N-methyl-N-ethyl aniline, N-methylmorpholine, tetramethylenediamine,oligomeric oxolanyl propanes (OOPs), 2,2-bis-(4-methyl dioxane), andbistetrahydrofuryl propane. A mixture of one or more randomizingmodifiers also can be used. The ratio of the modifier to the monomerscan vary from a minimum as low as 0 to a maximum as great as about 4000millimoles, preferably about 0.01 to 3000 millimoles, of modifier perhundred grams of monomer currently being charged into the reactor. Asthe modifier charge increases, the percentage of 1,2-microstructure(vinyl content) increases in the conjugated diene contributed monomerunits in the surface layer of the polymer nano-particle. The1,2-microstructure content of the conjugated diene units is preferablybetween about 5% and 95%, and preferably less than about 35%.

Without being bound by theory, it is believed that an exemplary micellewill be comprised of ten to five hundred multiblock polymers yielding,after crosslinking, a nano-particle having a M_(w) of between about5,000 and 10,000,000, preferably between about 5,000 and 4,500,000.

Structural Modifications

In an alternative embodiment, at least one layer of the polymernano-particle includes a copolymer including at least one alkenylbenzenemonomer unit and at least one conjugated diene monomer unit. Thecopolymer may be random or ordered. In one such embodiment the copolymerlayer includes a SBR rubber. Herein throughout, references to a poly(conjugated diene) layer are understood to include copolymers of thetype described here.

Similarly, the density of the nanoparticle may be controlled byincluding monoblock, diblock, and/or multiblock polymer chains in themicelles. One method for forming such polymer chains includes forming afirst polymer in the hydrocarbon solvent. After formation of the firstpolymer, a second monomer is added to the polymerization, along withadditional initiator. The second monomer polymerizes onto the firstpolymer to form a living diblock polymer as well as forming a separatesecond polymer which is a living mono-block polymer. A third polymer maythen be added along with additional initiator. The third polymer wouldpolymerize onto the diblock polymer to form a multi-block onto themonoblock polymer to form a diblock, as well as forming a third polymerwhich is a living monoblock polymer. The multiblock polymer contains atleast a first end block that is soluble in the dispersion solvent, and asecond end block which is less soluble in the dispersion solvent,preferably the vinyl-substituted aromatic hydrocarbon monomer.

Without being bound by theory, it is believed that a large number ofmono-block polymer chains in the core of the nano-particle results inand less entanglement of the tails of the diblock and multiblock chains.The resultant surface layer thus may have a brush-like structure.

The mono-block polymer preferably has M_(w) between about 1,000 and1,000,000, more preferably between about 5,000 and 100,000. Themulti-block polymer preferably has M_(w) of about 1,000 to 1,000,000more preferably between about 5,000 and 100,000. The di-block polymerpreferably has a Mw of about 1,000 to 1,000,000, more preferably betweenabout 5,000 and 100,000.

The density of the surface layers of the nano-particles may becontrolled by manipulating the ratio of multiblock to diblock tomono-block polymer chains. This ratio may be manipulated by altering theamount of initiator added during each step of the polymerizationprocess. For example, a greater amount of initiator added during thefirst polymerization step than added during subsequent polymerizationsteps would favor multiblock formation over mono-block formation,resulting in a high density surface layer. Conversely, a greater amountof initiator added during the subsequent polymerization steps than addedduring the first polymerization step would favor mono-block or diblockformation over multi-block formation, resulting in a low-density surfacelayer. The ratio of the initiator added during the subsequentpolymerization steps to that added during the first polymerization stepcan range from about 0 to 10.

Hydrogenation of a Nano Particle Surface Layer

After micelle formation, or alternatively, after crosslinking, polydieneblocks, for example, may be hydrogenated to form a desired surfacelayer. Furthermore, one or more poly (conjugated diene) blocks can beselectively hydrogenated while leaving additional poly (conjugateddiene) blocks non-hydrogenated. A hydrogenation step may be carried outby methods known in the art for hydrogenating polymers, particularlypolydienes. A preferred hydrogenation method includes placing thecrosslinked nano-particles in a hydrogenation reactor in the presence ofa catalyst. After the catalyst has been added to the reactor, hydrogengas (H₂) is charged to the reactor to begin the hydrogenation reaction.The pressure is adjusted to a desired range via addition of H₂,preferably between about 10 and 3000 kPa, more preferably between about50 and 2600 kPa. H₂ may be charged continuously or in individual chargesuntil the desired conversion is achieved. Preferably, the hydrogenationreaction will reach at least about 20% conversion, more preferablygreater than about 85% conversion. The conversion reaction may bemonitored by H¹ NMR.

Preferred catalysts include known hydrogenation catalysts such as Pt,Pd, Rh, Ru, Ni, and mixtures thereof. The catalysts may be finelydispersed solids or absorbed on inert supports such as carbon, silica,or alumina. Especially preferred catalysts are prepared from nickeloctolate, nickel ethylhexanoate, and mixtures thereof.

The layers formed by an optional hydrogenation step will vary dependingon the identity of the monomer units utilized in the formation of poly(conjugated diene) blocks. For example, if a poly(conjugated diene)block contains 1,3-butadiene monomer units, the resultant nano-particlelayer after hydrogenation will be a crystalline poly(ethylene) layer. Inanother embodiment, a layer may include both ethylene and propyleneunits after hydrogenation if the non-hydrogenated poly (conjugateddiene) block contains isoprene monomer units. It should be noted thatthe non-hydrogenated poly (conjugated diene) block may contain a mixtureof conjugated diene monomer units, resulting in a mixture of monomerunits after hydrogenation.

Initiators and Functionalized Nano-Particles

The present inventive process is preferably initiated via addition ofanionic initiators that are known in the art as useful in thecopolymerization of diene monomers and vinyl aromatic hydrocarbons.Exemplary organo-lithium catalysts include lithium compounds having theformula R(Li)_(x), wherein R represents a C₁-C₂₀ hydrocarbyl radical,preferably a C₂-C₈ hydrocarbyl radical and x is an integer from 1 to 4.Typical R groups include aliphatic radicals and cycloaliphatic radicals.Specific examples of R groups include primary, secondary, and tertiarygroups, such as n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, etc.

Specific examples of exemplary initiators include ethyllithium,propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, andthe like; aryllithiums, such as phenyllithium, tolyllithium, and thelike; alkenyllithiums such as vinyllithium, propenyllithium, and thelike; alkylene lithium such as tetramethylene lithium, pentamethylenelithium, and the like. Among these, n-butyllithium, sec-butyllithium,tert-butyllithium, tetramethylene lithium, and mixtures thereof arepreferred. Other suitable lithium inititators include one or more of:p-tolyllithium, 4-phenylbutyl lithium, 4-butylcyclohexyl lithium,4-cyclohexylbutyl lithium, lithium dialkyl amines, lithium dialkylphosphines, lithium alkyl aryl phosphine, and lithium diaryl phosphines.

Functionalized lithium initiators are also contemplated as useful in thepresent copolymerization. Preferred functional groups include amines,formyl, carboxylic acids, alcohols, tin, silica, and mixtures thereof.

Especially preferred initiators are amine-functionalized initiators,such as those that are the reaction product of an amine, an organolithium and a solubilizing component. The initiator has the generalformula:(A)Li(SOL)_(y)where y is from about 1 to about 3; SOL is a solubilizing componentselected from the group consisting of hydrocarbons, ethers, amines ormixtures thereof; and, A is selected from the group consisting of alkyl,dialkyl and cycloalkyl amine radicals having the general formula:

and cyclic amines having the general formula:

where R¹ is selected from the group consisting of alkyls, cycloalkyls oraralkyls having from 1 to about 12 carbon atoms, and R² is selected fromthe group consisting of an alkylene, substituted alkylene, oxy- orN-alkylamino-alkylene group having from about 3 to about 16 methylenegroups. An especially preferred functionalized lithium initiator ishexamethylene imine propyllithium.

Tin functionalized lithium initiators may also be preferred as useful inthe present invention. Suitable tin functionalized lithium initiatorsinclude tributyl tin lithium, trioctyl tin lithium, and mixturesthereof.

Anionic initiators generally are useful in amounts ranging from about0.01 to 60 millimoles per hundred grams of monomer charge.

A nano-particle including multiblock polymers initiated with afunctionalized initiator may include functional groups on the surface ofthe nano-particle. For example, when block polymers are initiated byhexamethylene imine propyllithium, the initiator residue remaining atthe beginning of the polymer chain will contain an amine group. Once thepolymer chains have aggregated and have been crosslinked, the resultantnano-particles will contain amine groups on or near the nano-particlesurface.

An exemplary nano-particle formed from copolymers initiated by afunctionalized tin lithium initiator may have a crosslinkedalkenylbenzene core, for example polystyrene, and a surface layerincluding at least a poly(conjugated diene), for example 1,3-butadiene.The surface layer will also include a functionalized initiator residueat the individual chain ends (i.e., tin).

Polymer Nano-Particle Applications

A variety of applications are contemplated for use in conjunction withthe nano-particles of the present invention. Furthermore, the severalmechanisms described herein for modifying the nano-particles render themmore suitable for different applications. All forms of the presentinventive nano-particles are, of course, contemplated for use in each ofthe exemplary applications and all other applications envisioned by theskilled artisan.

General Rubber

After the polymer nano-particles have been formed, they may be blendedwith a rubber to improve the physical characteristics of the rubbercomposition. Nano-particles are useful modifying agents for rubbersbecause they are discrete particles which are capable of dispersinguniformly throughout the rubber composition, resulting in uniformity ofphysical characteristics. Furthermore, certain of the present polymernano-particles are advantageous because various layers includingpoly(conjugated diene), especially vinyl-modified poly(conjugateddiene), are capable of bonding with a rubber matrix due to theaccessibility of the double bonds in the poly(conjugated diene).

The present polymer nano-particles are suitable for modifying a varietyof rubbers including, but not limited to, random styrene/butadienecopolymers, butadiene rubber, poly(isoprene), nitrile rubber,polyurethane, butyl rubber, EPDM, and the like. Advantageously, theinclusion of the present nano-particles have demonstrated rubbers havingimproved tensile and tear strength of at least about 30% over a rubbermodified with non-spherical copolymers.

Furthermore, nano-particles with hydrogenated layers may demonstrateimproved compatibility with specific rubbers. For example,nano-particles including a hydrogenated polyisoprene layer maydemonstrate superior bonding with and improved dispersion in an EPDMrubber matrix due to the compatibility of hydrogenated isoprene withEPDM rubber.

Additionally, nano-particles with copolymer layers may demonstrateimproved compatibility with rubbers. The copolymer tails within a layerof the nano-particles may form a brush-like surface. The hostcomposition is then able to diffuse between the tails allowing improvedinteraction between the host and the nano-particles.

Hard Disk Technology

Hydrogenated nano-particles prepared in accordance with the presentinvention may also find application in hard disk technology.

Disk drive assemblies for computers traditionally include a magneticstorage disk coaxially mounted about a spindle apparatus that rotates atspeeds in excess of several thousand revolutions per minute (RPM). Thedisk drive assemblies also include a magnetic head that writes and readsinformation to and from the magnetic storage disk while the magneticdisk is rotating. The magnetic head is usually disposed at the end of anactuator arm and is positioned in a space above the magnetic disk. Theactuator arm can move relative to the magnetic disk. The disk driveassembly is mounted on a disk base (support) plate and sealed with acover plate to form a housing that protects the disk drive assembly fromthe environmental contaminant outside of the housing.

Serious damage to the magnetic disks, including loss of valuableinformation, can result by introducing gaseous and particulatecontaminates into the disk drive assembly housing. To substantiallyprevent or reduce the introduction of gaseous and particulatecontaminants into the disk drive housing, a flexible sealing gasket isdisposed between the disk drive mounting base (support) plate and thedisk drive assembly housing or cover plate. A sealing gasket is usuallyprepared by punching out a ring-shaped gasket from a sheet of curedelastomer. The elastomeric gasket obtained is usually attached to thebase plate of the disk drive assembly mechanically, such as affixing thegasket with screws, or adhesives. The hydrogenated nano-particles, whencompounded with a polyalkylene and a rubber, demonstrate a tensilestrength comparable to that necessary in hard disk drive compositions.

Thermoplastic Gels

Nano-particles prepared in accord with the present invention, whetherhydrogenated or non-hydrogenated may also be blended with a variety ofthermoplastic elastomers, such as SEPS, SEBS, EEBS, EEPE, polypropylene,polyethylene, polystyrene, and mixtures thereof. For example,nano-particles with hydrogenated isoprene layers may be blended with aSEPS thermoplastic to improve tensile strength and thermostability.These blends of thermoplastic elastomer and nano-particles wouldtypically be extended as known in the art. For example, suitableextenders include extender oils and low molecular weight compounds orcomponents. Suitable extender oils include those well known in the artsuch as naphthenic, aromatic and paraffinic petroleum oils and siliconeoils.

Examples of low molecular weight organic compounds or components usefulas extenders in compositions of the present invention are low molecularweight organic materials having a number-average molecular weight ofless than 20,000, preferably less than 10,000, and most preferably lessthan 5000. Although there is no limitation to the material which may beemployed, the following is a list of examples of appropriate materials:

Softening agents, namely aromatic naphthenic and □araffinic softeningagents for rubbers or resins;

Plasticizers, namely plasticizers composed of esters including phthalic,mixed pthalic, aliphatic dibasic acid, glycol, fatty acid, phosphoricand stearic esters, epoxy plasticizers, other plasticizers for plastics,and phthalate, adipate, scbacate, phosphate, polyether and polyesterplasticizers for NBR;

Tackifiers, namely coumarone resins, coumaroneindene resins, terpenephenol resins, petroleum hydrocarbons and rosin derivative;

Oligomers, namely crown ether, fluorine-containing oligomers,polybutenes, xylene resins, chlorinated rubber, polyethylene wax,petroleum resins, rosin ester rubber, polyalkylene glycol diacrylate,liquid rubber (polybutadiene, styrene/butadiene rubber,butadiene-acrylonitrile rubber, polychloroprene, etc.), siliconeoligomers, and poly-a-olefins;

Lubricants, namely hydrocarbon lubricants such as paraffin and wax,fatty acid lubricants such as higher fatty acid and □ydroxyl-fatty acid,fatty acid amide lubricants such as fatty acid amide andalkylene-bisfatty acid amide, ester lubricants such as fatty acid-loweralcohol ester, fatty acid-polyhydrie alcohol ester and fattyacid-polyglycol ester, alcoholic lubricants such as fatty alcohol,polyhydric alcohol, polyglycol and polyglycerol, metallic soaps, andmixed lubricants; and,

Petroleum hydrocarbons, namely synthetic terpene resins, aromatichydrocarbon resins, aliphatic hydrocarbon resins, aliphatic or alicyclicpetroleum resins, polymers of unsaturated hydrocarbons, and hydrogenatedhydrocarbon resins.

Other appropriate low-molecular weight organic materials includelatexes, emulsions, liquid crystals, bituminous compositions, andphosphazenes. One or more of these materials may be used in asextenders.

Surface functionalized nano-particles prepared in accordance with thepresent invention, whether hydrogenated or non-hydrogenated, may also becompounded with silica containing rubber compositions. Including surfacefunctionalized nano-particles in silica containing rubber compositionshas been shown to decrease the shrinkage rates of such silica containingrubber compositions. Functionalized nano-particles may be compounded insilica compositions in concentrations up to about 50 wt % of the totalcomposition, more preferably up to about 40 wt % most preferably up toabout 30 wt %.

Tire Rubber

One application for such rubber compounds is in tire rubberformulations.

Vulcanizable elastomeric compositions of the invention are prepared bymixing a rubber, a nanoparticle composition, with a reinforcing fillercomprising silica, or a carbon black, or a mixture of the two, aprocessing aid and/or a coupling agent, a cure agent and an effectiveamount of sulfur to achieve a satisfactory cure of the composition.

The preferred rubbers are conjugated diene polymers, copolymers orterpolymers of conjugated diene monomers and monovinyl aromaticmonomers. These can be utilized as 100 parts of the rubber in the treadstock compound, or they can be blended with any conventionally employedtreadstock rubber which includes natural rubber, synthetic rubber andblends thereof. Such rubbers are well known to those skilled in the artand include synthetic polyisoprene rubber, styrene-butadiene rubber(SBR), styrene-isoprene rubber, styrene-isoprene-butadiene rubber,butadiene-isoprene rubber, polybutadiene, butyl rubber, neoprene,acrylonitrile-butadiene rubber (NBR), silicone rubber, thefluoroelastomers, ethylene acrylic rubber, ethylene-propylene rubber,ethylene-propylene terpolymer (EPDM), ethylene vinyl acetate copolymer,epicholrohydrin rubber, chlorinated polyethylene-propylene rubbers,chlorosulfonated polyethylene rubber, hydrogenated nitrile rubber,terafluoroethylene-propylene rubber, and the like.

Examples of reinforcing silica fillers which can be used in thevulcanizable elastomeric composition include wet silica (hydratedsilicic acid), dry silica (anhydrous silicic acid), calcium silicate,and the like. Other suitable fillers include aluminum silicate,magnesium silicate, and the like. Among these, precipitated amorphouswet-process, hydrated silicas are preferred. Silica can be employed inthe amount of about one to about 100 parts per hundred parts of theelastomer (phr), preferably in an amount of about 5 to 80 phr and , morepreferably, in an amount of about 30 to about 80 phrs. The useful upperrange is limited by the high viscosity imparted by fillers of this type.Some of the commercially available silica which can be used include, butare not limited to, HiSil® 190, HiSil® 210, HiSil® 215, HiSil® 233,HiSil® 243, and the like, produced by PPG Industries (Pittsburgh, Pa.).A number of useful commercial grades of different silicas are alsoavailable from DeGussa Corporation (e.g., VN2, VN3), Rhone Poulenc(e.g., Zeosil® 1165MP0, and J.M. Huber Corporation.

Including surface functionalized nano-particles in silica containingrubber compositions has been shown to decrease the shrinkage rates ofsuch silica containing rubber compositions. Functionalizednano-particles may be compounded in silica compositions inconcentrations up to about 30 wt % of the total composition, morepreferably up to about 40 wt %, most preferably up to about 50 wt %.

The rubber can be compounded with all forms of carbon black, optionallyadditionally with silica. The carbon black can be present in amountsranging from about one to about 100 phr. The carbon black can includeany of the commonly available, commercially-produced carbon blacks, butthose having a surface are of at least 20 m²/g and, or preferably, atleast 35 m²/g up to 200 m²/g or higher are preferred. Among usefulcarbon blacks are furnace black, channel blacks, and lamp blacks. Amixture of two or more of the above blacks can be used in preparing thecarbon black products of the invention. Typical suitable carbon blackare N-110, N-220, N-339, N-330, N-352, N-550, N-660, as designated byASTM D-1765-82a.

Certain additional fillers can be utilized including mineral fillers,such as clay, talc, aluminum hydrate, aluminum hydroxide and mica. Theforegoing additional fillers are optional and can be utilized in theamount of about 0.5 phr to about 100.

Numerous coupling agent and compatibilizing agent are know for use incombining silica and rubber. Among the silica-based coupling andcompatibilizing agents include silane coupling agents containingpolysulfide components, or structures such as, for example,trialkoxyorganosilane polysulfides, containing from about 2 to about 8sulfur atoms in a polysulfide bridge such as, for example,bis-(3-triethoxysilylpropyl) tetrasulfide (Si69),bis-(3-triethoxysilylpropyl) disulfide (Si75), and those alkylalkoxysilanes of the such as octyltriethoxy silane, and hexyltrimethoxysilane.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various vulcanizablepolymer(s) with various commonly used additive materials such as, forexample, curing agents, activators, retarders and acceleratorsprocessing additives, such as oils, resins, including tackifying resins,plasticizers, pigments, additional filers, fatty acid, zinc oxide,waxes, antioxidants, anti-ozonants, and peptizing agents. As known tothose skilled in the art, depending on the intended use of the sulfurvulcanizable and sulfur vulcanized material (rubbers), the additivesmentioned above are selected and commonly used in the conventionalamounts.

Specifically, the above-described nano-particle containing rubbercompounds are contemplated for use in rubber compounds used to make tiretreads and side walls due to the enhanced reinforcement capabilities ofthe present nano-particles. The higher dynamic modulus (G′) and itslower temperature dependence along with the lower hystersis values athigh temperatures leads to improved cornering, handling, dry, snow, andwet traction, rolling resistance, dispersion, and aging properties ofthe resultant tire compositions. Tin-functionalized nano-particles areespecially suited for use in tire compositions. Improved agingproperties, thermal aging (high temperature), or mechanical aging(static or dynamic deformation cycles), include retention of the G′modulus, hysteresis, mechanical strengths, etc. Tin-functionalizednano-particles are especially suited for use in tire compositions.Nano-particles including a copolymer layer are also suitable for use insuch tire compositions, because the longer copolymer chains in the layerlead to greater diffusion of the host rubber composition into thesurface layer of the nano-particle. Of course, a functionalizednano-particle having at least one copolymer layer, i.e., the combinationof the two alternatives may be most beneficial.

Engineering Plastic and Others

Similarly, the nano-particles can be added into typical plasticmaterials, including polyethylene, polypropylene, polystyrene,polycarbonate, nylon, polyimides, etc. to for example, enhance impactstrength, tensile strength and damping properties.

Of course, the present inventive nano-particles are also suited to otherpresently existing applications for nano-particles, including themedical field, e.g. drug delivery and blood applications, informationtechnology, e.g. quantum computers and dots, aeronautical and spaceresearch, energy, e.g., oil refining, and lubricants.

Engine Mount, ETC

Another application for such rubbers is in situations requiring superiordamping properties, such as engine mounts and hoses (e.g. airconditioning hoses). Rubber compounds of high mechanical strength, superdamping properties, and strong resistance to creep are demanded inengine mount manufacturers. In engine mounts, a rubber, because it sitsmost of its life in a packed and hot position, requires very goodcharacteristics. Utilizing the nano-particles within selected rubberformulations can improve the characteristics of the rubber compounds.

The present invention now will be described with reference tonon-limiting examples. The following examples and tables are presentedfor purposes of illustration only and are not to be construed in alimiting sense.

EXAMPLES Preparation of Multi-Layer Nano Particles

An 8 L reactor equipped with external jacket heating and internalagitation was used for all polymerizations. 1,3-Butadiene was used as a22.0 or 21.1 wt % solution in hexane (Bridgestone/Firestone Polymer Co.,Akron, Ohio). Styrene was used as a 33.0 wt. % solution in hexane(Bridgestone/Firestone Polymer Co., Akron, Ohio), and

n-butyllithium was used as a 15 wt % solution in hexane(Bridgestone/Firestone Polymer Co., Akron, Ohio). An antioxidantbutylated hydroxytoluene (BHT), (Aldrich Chem. Co., Milwaukee, Wis.) wasused as an approximately 17 wt % solution in hexane. Technical gradedivinylbenzene (DVB), (80% as a mixture of isomers, Aldrich) was passedthrough a column of inhibitor remover under N₂ before use. Neatbis-oxalanyl propane (OOPs), (Aldrich) was similarly treated and used asa 1.6 M solution in hexane, stored over calcium hydride.

Example 1

The reactor was first charged with 2.3 kg of hexane. The reactor wasthen charged with 517 g butadiene/hexane blend that contained 22 wt %butadiene, and the batch was heated to 57° C. After the temperaturestabilized, polymerization was initiated with 5.4 mL of a 1.5 M solutionof n-butyl lithium in hexane. The reactor batch temperature wasmaintained at 57° C. for the duration of the polymerization. After 2hours, (when the reaction was finished) the reactor was charged with 4.5kg of isoprene/hexane blend that contained 15% isoprene. After 1.5hours, the reactor was charged with 453 g of a styrene/hexane blend thatcontained 33 wt % styrene. After an additional 1.5 hours, the reactorwas charged with 50 mL of divinyl benzene. The reactor was maintained at57° C. for a 2-hour period and then discharged. The product was droppedinto an acetone/isopropanol (˜95/5) blend, and dried. GPC analysis ofthe product showed that the molecular weight (M_(w)) of the particlepolymer is 954,390. The polydispersity of the product is 1.10. TEManalysis showed that the average particle size was ˜30 nm, and thedispersity of the particle size was about 1.1 (see FIG. 2). Thestructure of the particle contains a polystyrene-core, a poly-isoprenelayer, and a poly-butadiene surface layer.

Example 2

A 4 L polymerization reactor was used for the preparation. The reactorwas first charged with 3 L of a nano-particle/hexane solution,containing 10 wt % of example 1. The reactor was then charged with 75 mLof a Ni catalyst solution, which was made according to the followingprocedure.

111 mL of nickel octolate (8 wt % in hexane), 37 mL hexane, and 06 mL ofcyclohexene were charged to a 1 liter N₂ purged bottle. Then, the bottlewas placed into a dry ice bath. A charge of 266.4 mL of tributylaluminum (0.68 M in hexane) was slowly added into the bottle while keptcool.

The hydrogenation reactor, containing polymer product and catalyst wasthen heated to 120° C. After the temperature stabilized, thehydrogenation was initialized by charging high pressure H₂ gas into thereactor to about 792 kPa. After about 15 minutes, the pressure droppedas the H₂ began to react. The reactor was again recharged to about 792kPa. The procedure was then repeated until the butadiene hydrogenationconversion reached about 95%, based on H¹ NMR analysis. The reactor wasthen cooled and the product dropped into isopropanol solvent. Theobtained polymer particles were dried in vacuum for 2 days at 23° C.

The procedure was repeated until the isoprene hydrogenation conversionreached 100% based on H¹ NMR analysis. TEM analysis showed that theaverage particle size was ˜35 nm, and the dispersity was about 1.1 (seeFIG. 3). The structure of the particle contained a polystyrene core, apoly(ethylene-co-propylene) layer, and a polyethylene shell.

Example 3

The reactor was first charged with 517 g of hexane. The reactor wascharged with 340 g styrene/hexane blend containing 33 wt % styrene, andthe batch was heated to 57° C. After the temperature had stabilized,polymerization was initiated with 5.4 mL of a 1.5 M solution ofn-butyllithium in hexane. The reactor batch temperature was maintainedat 57° C. for the duration of the polymerization. After 1.5 hours, (whenthe reaction was finished), the reactor was charged with 1.0 kg ofbutadiene/hexane blend that contained 22 wt % butadiene. After another1.5 hours, the reactor was charged with 340 g of styrene/hexane blendthat contained 33 wt % styrene. After an additional 1.5 hour reaction,the reactor was charged with 1.8 kg hexane. After 20 minutes, thereactor was charged with 50 mL of DVB for the crosslinking reaction. Thereactor was maintained at 57° C. for another 1.5 hour period, thendischarged. The product was dropped into acetone/isopropanol (˜95/5)blend, and dried. GPC analysis of the product showed that the molecularweight (M_(w)) of the particle polymer was 3,271,180. The polydispersitywas 1.08. TEM analysis showed that the average particle size was ˜35 nm,and the dispersity of the particle size was about 1.1 (see FIG. 4). Thestructure of the particle contained the polystyrene core, thepolybutadiene layer, and a polystyrene surface layer.

Examples 4-6

Three kinds of rubber compositions were prepared according to theformulation shown in Tables 1 and 2 by selectively using the synthesizedonion like polymer particles (i.e., example 1) to replace 10 parts ofbutadiene rubber in the compound formulation. In each sample, a blend ofthe ingredients was kneaded by a method listed in Table 3. The finalstock was sheeted and molded at 160° C. for about 30 minutes.

As shown in Table 4, the test compounds exhibited well balanced physicalproperties. At least, the tensile strength, dynamic modulus and dampingproperties were improved over that of the comparative compounds. TABLE 1Composition for Master Batch Component Pbw Polybutadiene (HX 301) 100.00Carbon black (N343) 50.00 Aromatic oil 15.00 Zinc oxide 3.00 Hydrocarbonresin (tackifiers) 2.00 Santoflex 13 (antioxidants) 0.95 Stearic acid2.00 Wax 1.00

TABLE 2 Composition for Final Batch Additional component added to masterbatch of table 14 Pbw Sulfur ˜1.30 Cyclohexyl-benzothiazole sulfenamide(accelerator) 1.40 Diphenylguanidine (accelerator) 0.20

TABLE 3 Mixing Conditions Mixer: 300 g Brabender Agitation speed: 60 rpmMaster Batch Stage Initial Temperature 110° C.   0 minutes Chargingpolymers 0.5 minutes Charging oil and carbon black 5.0 minutes DropFinal Batch Stage Initial Temperature 75° C.  0 seconds Charging masterstock 30 seconds Charging curing agent and accelerators 75 seconds Drop

TABLE 4 Experimental results of Multi-Layer Nano-particles: Example 4(control) 5 6 Test Example 3 10 polymers Example 1 10 Butadiene 100 9090 Carbon 50 50 50 black Aromatic 15 15 15 oil Shore A 22° C. (3seconds) 56.1 60.7 58.4 100° C. (3 seconds) 53.9 56.1 55.6 Ring Tensile23° C. Tb (kPa) 13,511 14,200 12,926 Eb (%) 494 485 483 M300 925 1060950 M50 151 187 166 100° C. Tb(kPa) 6842 8068 7200 Eb (%) 355 383 362M300 780 835 806 M50 122 135 130 Ring Tear Strength (kg/cm) 34.01 37.0538.31 Travel (%) 170° C. 439 437 453 Tg of compound (tan δ) −75 −75 −75Dynastat M′ 50° C. (mPa) 6.7711 8.7605 7.6634 M′ 23° C. (mPa) 7.823310.6590 9.1403 M′ 0° C. (mPa) 9.6050 14.1940 11.6610 M′ −20° C. (mPa)11.3360 15.8320 13.000 tan δ 50° C. 0.18533 0.20372 0.19581 tan δ 23° C.0.21062 0.22369 0.22109 tan δ 0° C. 0.23358 0.23813 0.24245 tan δ −20°C. 0.25302 0.25763 0.26128

The invention has been described with reference to the exemplaryembodiments. Modifications and alterations will occur to others uponreading and understanding the specification. The invention is intendedto include such modifications and alterations insofar as they comewithin the scope of the disclosure and claims.

1-23. (canceled)
 24. A polymeric nanoparticle comprising at least threelayers, the layers comprising: the first layer consisting essentially ofpolymerized alkenylbenzene monomers crosslinked by at least onecrosslinking agent; and, the second and third layers independentlycomprising at least one monomer chosen from conjugated dienes,alkenylbenzenes, alkylenes, ethylene oxide, methyl methacrylate,nitriles, and acrylates; wherein the nanoparticle has a mean averagediameter of less than about 100 nm.
 25. The nanoparticle of claim 24,wherein alkenylbenzene monomers of the first layer are polystyrene. 26.The nanoparticle of claim 24, wherein the at least one crosslinkingagent is divinylbenzene.
 27. The nanoparticle of claim 24, wherein atleast one of the second and third layers is formed of a random copolymerof at least two monomers chosen from conjugated dienes, alkenylbenzenes,alkylenes, ethylene oxide, methyl methacrylate, nitriles, and acrylates.28. The nanoparticle of claim 27, wherein the at least two monomers arechosen from conjugated dienes and alkenylbenzenes.
 29. The nanoparticleof claim 27, wherein the second layer is formed of a random copolymer ofat least two monomers chosen from conjugated dienes, alkenylbenzenes,alkylenes, ethylene oxide, methyl methacrylate, nitriles, and acrylates.30. The nanoparticle of claim 29, wherein the at least two monomers arechosen from conjugated dienes and alkenylbenzenes.
 31. The nanoparticleof claim 24, wherein the at least one monomer of the third layer ischosen from conjugated dienes.
 32. The nanoparticle of claim 31, whereinthe third layer is hydrogenated.
 33. The nanoparticle of claim 24,wherein the first layer consists essentially of polymerized styrenemonomers crosslinked by divinylbenzene, the second layer comprisesstyrene and 1,3-butadiene monomers, and the third layer comprises1,3-butadiene.
 34. The nanoparticle of claim 33, wherein the styrene and1,3-butadiene monomers of the second layer are randomized.
 35. Thenanoparticle of claim 24, wherein the nanoparticle has a mean averagediameter of less than about 75 nm.
 36. The nanoparticle of claim 35,wherein the nanoparticle has a mean average diameter of less than about50 nm.
 37. The nanoparticle of claim 24, wherein the nanoparticle has aM_(w) of about 5,000 to about 4,500,000.